Contour lines are those seemingly endless squiggly brown lines on the map
picture. Each of these lines is drawn on an exact elevation on that "terrain
feature." The distance between the lines are a presentation of the vertical
distance
between the lines. The vertical distance between the lines is the "contour
interval." In our example, the contour interval is 40 feet, which means that
between each of those brown lines on the map to the one next to it is an
elevation change of 40 feet. But, is it 40 feet up or down? We will get more
into this later.